A cage protein is a protein to form a macromolecule having a molecular weight of dozens to hundreds times of a monomer by self-assembly properties of a low molecular weight monomer. Virus capsid protein, ferritin, heat shock protein, Dps protein belong to the cage protein in nature. Each monomer to form the cage protein has a very regular and precise interaction with adjacent monomer and inside of the cage is empty. Since the inside of the cage is isolated from the outside by the nature such as the container of the cage protein, the cage protein is frequently used as a drug delivery system in the field of medicine.
Specially, a small heat shock protein, HSP is classified into five families of HSP100, HSP90, HSP70, HSP60 and smHSP according to a molecular weight. These are known to be induced by stress stimuli including nutritional deficiencies, metabolic disorders, oxygen radicals and cellular pathogen infection (Welch May, 1993, Scientific American 56-64; Young, 1990, Annu. Rev. Immunol. 8: 401-420; Craig, 1993, SCIENCE 260: 1902-1903; Gething et al., 1992, Nature 355: 33-45; and Lindquist et al., 1988, Annu. Rev. Genetics 22: 631-677).
Meanwhile, proteases regulate diverse cellular functions in a wide range and these functions are done through the degradation of bioactive material. Thus, function and role of the proteases are very important to vital phenomenon of all living things. For example, deficiency, lack or over-expression of a specific protease lead to a significant result, that is cancer, arthritis, neurodegenerative diseases, cardiovascular, autoimmune inflammatory diseases, and so on may occur. Thus, proteases and substrates thereof are major targets for a new drug development and a matter of interest in the pharmaceutical industry.
Roles of proteases in vitro and in vivo are actively studied due to various roles of proteases and recently completed genome projects. According to the human genome projects, more than about 500 of human genes were found to be related to proteases. Recently, it has been newly disclosed that protease plays a pivot role and provides cause in human diseases such as cancer and Alzheimer's disease.
For example, metal matrix protease (MMP) has been recognized as a factor to degrade extracellular matrix in the cell and in vivo in the past, however, MMP were identified to be involved in integrin signaling and cell movement according to degradation of pericellular matrix through various studies. In addition, MMP has been disclosed to play an important role in the cancer growth such as angiogenesis, tumor cell invasion and metastasis.
Apoptosis has been also in the spotlight in the field of life science in the last decade and known to play an important role in embryonic development, immune response and tissue homeostasis (Vaux, D. L. et al. 1999). In case there occurs something wrong with apoptosis, incurable diseases such as cancer or neurodegenerative disorder may occur (Nicholson, D. W. 1996). A large number of enzymes are involved in apoptosis. Among them, apoptosis typically begins by caspase which is protease activated after activation of death receptor.
As described above, physiological functions of various proteases will be newly illuminated according to disclosure of new substrates, thereby target proteins for a new drug are expected to be developed.
However, there are no methods to detect by imaging activity of a specific protease, or non-invasive imaging techniques for detecting expression level of proteases in vivo, so development of related technology is urgently required. For representative methods of measurement of protease, there are 2-D gels and multi-performance liquid chromatography, Enzyme-Linked ImmunoSorbent Assay (ELISA) or a method to measure peak shift with spectroscopy by combining a fluorescent substrate with protease-specific peptide substrate.
However, these methods require multi-step protocol to measure, especially if a peptides itself is used, synthesis and purification processes are cumbersome and costs high. There are also disadvantages of cytotoxicity and significantly low cell permeability.